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Abstract:

One embodiment of the present disclosure is directed to a method used in
the making of a dental restoration, which comprises the steps of
determining a tooth flat at a patient's tooth, and evaluating the tooth
flat to provide a geometric characteristic data of the first tooth flat.
The characteristic data are used to provide a computer model of a jaw
motion under occlusal contact between teeth in the patient's upper and
lower jaws. In one embodiment, the method helps facilitating the
preparation of dental restorations.

Claims:

1. A method comprising the steps of: determining a first tooth flat at a
representation of a first patient's tooth; evaluating the first tooth
flat to provide characteristic data representing at least one geometric
characteristic of the first tooth flat; using the characteristic data to
calculate a computer model of the patient's possible jaw motion under
occlusal contact between teeth in the patient's upper and lower jaws.

2. The method of claim 1, wherein the step of evaluating the first tooth
flat comprises recognizing of a substantially planar surface area of the
first tooth by a curvature of that surface area being within a
predetermined range and/or recognizing of a shaded surface area by its
shade differentiating from an adjacent surface area.

3. The method of claim 1, wherein the step of evaluating the first tooth
flat comprises manual recognition of the first tooth flat and optically
shading the first tooth flat.

4. The method of claim 1, wherein the step of evaluating the first tooth
flat comprises automatic recognition of the first tooth flat by use of a
computer.

5. The method of claim 1, further comprising the step of determining at
least one positional relationship between the upper and lower jaws in
which the upper and lower jaws are under occlusal contact.

6. The method of claim 5, wherein the step of determining a positional
relationship comprises detecting a second tooth flat at an opposite
second tooth on the basis of similar characteristic data between the
first and second teeth.

7. The method of claim 1, wherein the characteristic data comprises at
least one of an inclination angle of the flat in a reference coordinate
system; a position of the flat in the reference coordinate system; a
curvature of the flat; a surface roughness of the flat; a size of the
flat; and a shape of the flat.

8. The method of claim 7, further comprising the step of determining a
motion path representing a model of a possible movement of the jaws
relative to one another under occlusal contact, wherein the motion path
extends along a line between a first and a different second positional
relationship of the jaws.

9. The method of claim 7, further comprising the step of determining a
motion surface representing a model of a possible movement of the jaws
relative to one another under occlusal contact, wherein the motion
surface extends between at least three different positional relationships
between the jaws.

10. The method of claim 8, using the motion path or motion surface for
determining a shape of a least part of a dental restoration.

11. The method of claim 10, wherein at least a partial representation of
a tooth opposite of the dental restoration is virtually moved on the
motion path or on the motion surface to virtually carve away a volume of
a preliminary representation of the dental restoration.

12. The method of claim 1, further comprising the step of providing a
representation of a preliminary representation of a dental restoration.

13. The method of claim 1, comprising the steps of determining a
plurality of tooth flats at representations of a patient's teeth, and
evaluating the plurality of tooth flats to provide characteristic data
representing a multiplicity of geometric characteristics related to the
individual tooth flats.

14. A System for preparing a dental restoration, comprising software
adapted for performing the method of claim 1.

15. (canceled)

Description:

FIELD OF THE INVENTION

[0001] The invention relates to a method in the making of a dental
restoration, and in particular to a method of determining a jaw motion
which is possible under occlusal contact between teeth in the patient's
upper and lower jaws.

BACKGROUND ART

[0002] The shape of a dental restoration is typically determined dependent
on the shape of at least one tooth that neighbors a tooth or teeth to be
restored. Such a neighboring tooth may be an adjacent tooth of the tooth
to be restored in the same jaw or an opposite tooth of the tooth to be
restored in the opposing jaw. Further at least part of the shape of the
tooth to be restored may eventually be used to determine the shape of the
restoration if residual structure of that tooth is present.

[0003] Further for determining the shape of the dental restoration the
possible movements of the upper and lower jaws must typically be
accounted for, particularly when the jaws are closed so that at least one
tooth of the upper jaw is in contact with a tooth of the lower jaw. Such
a situation is typically referred to as the teeth being in "occlusal
contact" in dentistry. This is because opposing teeth in a patient's
mouth typically frequently contact each other in different positions
relative to one another, for example during chewing. Therefore a good fit
between the restoration and an opposing tooth or opposing teeth must be
ensured not only in one position but rather in various positions of the
jaws relative to one another. Further the jaws can typically be moved
relative to one another with the teeth remaining in occlusal contact, as
it also often occurs for example during chewing. Such a movement of the
jaws relative to one another with the teeth being in occlusal contact is
typically referred to as "articulation" in dentistry. Therefore for the
preparation of a dental restoration the articulation is typically
determined and simulated for precisely fitting the dental restoration to
one or more opposing teeth.

[0004] There are various methods for simulating the articulation, one of
which comprises manual articulation by use of a mechanical articulator.
Such a mechanical articulator typically reproduces the human upper and
lower jaws which are movably connected by a joint. The reproduced jaws
are further adapted to receive models of a patient's jaw that also
represent the patient's teeth so that the articulation can be simulated.
The dental restoration may be placed in a model to test its fit relative
to neighboring teeth under simulated articulation. The joint of such an
articulator is typically designed to resemble the mechanical interaction
of the bones forming the joint. That joint is typically referred to as
"temporomandibular joint" in dentistry. The mechanical interaction of
bone joints is more complex that a simple mechanical hinge, and in
particular may provide for a movement which deviates from an ideally
circular movement around a pivot axis as provided by a hinge. Further a
bone joint may also allow movements radially and axially from the pivot
axis. There are different articulators which resemble the
temporomandibular joint at different quality. Articulators that are
designed to more precisely resembling the temporomandibular joint are
often also more complex in use and more expensive than other articulators
having a simpler configuration.

[0005] Because the precision of a simulated articulation may be important
to provide a precisely fitting dental restoration approaches have been
developed which include the use of computers.

[0006] For example U.S. Pat. No. 6,431,871 B1 discloses a method which
comprises the steps of producing casts of the upper and lower jaw from an
impression, coordinating them using an articulator, coordinating
reference points on the jaw casts with the rotation axis of the
articulator, arranging the jaw casts in a measuring device for
determining the geometry of the tooth to be restored and the rotation
axis of the articulator by use of the reference points, digitizing the
jaw casts, and constructing the denture using CAD, and manufacturing the
denture using CAM.

[0007] US 2009/0068617 A1 discloses methods for acquiring and utilizing
time-based 3D jaw motion images to enhance the computer-aided design of
dental restorations. The 3D jaw motion images are used to provide a jaw
motion model for driving a motion simulation which is used in a
computer-aided design of a dental restoration.

[0008] Although existing approaches may provide certain advantages there
is still a need for facilitating the preparation of dental restorations
which precisely fit and cooperate with other teeth in a patient's mouth.
Desirably such dental restorations can be prepared largely outside of a
patient's mouth and require minimized or no mechanical finishing in shape
after placement in the patient's mouth. Further it is desirable that such
dental restorations are relatively inexpensive.

SUMMARY OF THE INVENTION

[0009] In one aspect the invention relates to a method in the making of a
dental restoration, and in particular to a method of determining an
articulation. The method comprises the steps of:

[0010] determining a first tooth flat at a representation of a first
patient's tooth;

[0011] evaluating the first tooth flat to provide characteristic data
representing at least one geometric characteristic of the first tooth
flat;

[0012] using the characteristic data to calculate a computer model of the
patient's possible jaw motion under occlusal contact between teeth in the
patient's upper and lower jaws.

[0013] An alternative method comprises the steps of:

[0014] determining a first tooth flat at a first patient's tooth;

[0015] evaluating the first tooth flat to provide characteristic data
representing at least one geometric characteristic of the first tooth
flat;

[0016] using the characteristic data to calculate a computer model of the
patient's possible jaw motion under occlusal contact between teeth in the
patient's upper and lower jaws.

[0017] The invention is advantageous in that it preferably facilitates the
preparation of a dental restoration. The invention may for example allow
for using one or more flats present at a patient's tooth or teeth to
obtain information about the articulation of that patient. As an
advantage such information about articulation may be directly calculated
from geometric characteristics of the flat(s) by use of the present
invention. Therefore the invention may be advantageous in that a
mechanical articulator may not be required. The invention preferably also
allows determining the articulation directly rather than indirectly via a
mechanical and/or virtual articulator. This is because articulators
typically simulate the temporomandibular joint and based on that
simulation the articulation is derived, whereas the invention preferably
does not require a simulation of the temporomandibular joint, but may
directly calculate the articulation based on the shape of the teeth.
Further the method of determining the articulation may be performed
remote from of the patient and without interaction with the patient, in
particular measuring of anatomic characteristics at the patient using a
face bow is preferably not be required in the method of the invention.
Further the invention may be advantageous in that it may help providing a
relatively inexpensive dental restoration because measuring efforts,
typically performed by the dentist, and manual determination of the
articulated, typically performed by a dental technician, may be
minimized.

[0018] The "calculation of the computer model of a possible jaw motion"
for the purpose of this specification preferably relates to the use of
the characteristic data in one or more computer instructions to provide
data which are suitable for geometrically defining the jaw motion. Such
data may for example comprise three-dimensional positions of an upper jaw
relative to a corresponding lower jaw, or of an upper tooth in an upper
jaw relative to a lower tooth in a corresponding lower jaw. Such data may
for further comprise direction vectors for describing a displacement
between an upper jaw relative to a corresponding lower jaw, or between an
upper tooth in an upper jaw relative to a lower tooth in a corresponding
lower jaw.

[0019] A "flat" as referred to in the present specification may be a
result of abrasion of two opposing teeth on each other, for example
during chewing action. It has been found that flats caused by abrasion
are typically present at teeth of most patient's. Such flats typically
differentiate by their curvature from the curvature of the flat
surrounding tooth structure, and are even in many cases substantially
planar. Also it has been found that a natural tooth typically is
substantially free of natural flats such that substantially all of the
present flats correspond to abrasion caused flats. It has further been
found that therefore abrasion caused tooth flats may be relatively
reliably identified.

[0020] A "possible jaw motion under occlusal contact between teeth in the
patient's upper and lower jaws" preferably refers to a movement of a
patient's jaws relative to one another that are enabled under constantly
maintaining the occlusal contact. In contrast there may be a movement
which is restricted under occlusal contact due to at least a tooth of
each jaw engaging and blocking that movement. The possible jaw motion
under occlusal contact between teeth in the patient's upper and lower
jaws may also generally be referred to as "articulation".

[0021] In one embodiment the representation of the patient's first tooth
is provided in a physical positive or negative model of the patient's
teeth. A negative model of the patient's teeth may correspond to a dental
impression taken in a patient's mouth. However the negative model may
further be manufactured in a material build-up process. The build-up
process may be controlled based on scan data obtained by intra-oral
scanning, for example. The physical model may further be a positive
plaster model which is, for example obtained from casting in the negative
model. Such a positive model may also be manufactured in a material
build-up process which may be controlled based on intra-oral scan data.

[0022] In another embodiment the representation of the patient's first
tooth is a computer model representing (for example in the form of
mathematically descriptive surface data) a surface of the patient's first
tooth. Such a computer model may represent one or more further teeth, for
example all teeth present in one or both jaws, and part of the gums.

[0023] In one embodiment the step of evaluating the first tooth flat
comprises recognizing of a substantially planar surface area of the first
tooth by a curvature of that surface area being within a predetermined
range. Further in this embodiment the step of evaluating the first tooth
flat may comprise recognizing a shaded surface area by its shade
differentiating from an adjacent surface area.

[0024] In another embodiment the step of evaluating the first tooth flat
comprises manual recognition of the first tooth flat and optically
shading the first tooth flat. For example the representation of the
patient's first tooth may be explored for a surface area which has a
certain shading relative to other surface areas, and a surface area
having such a shading may be identified as flat. The shading is
preferably provided on the tooth representation, for example manually
provided by a dentist or a dental technician by highlighting, for example
with a color. The shading may however in an alternative method be
provided on a natural tooth. The flats may thus be highlighted relative
to an adjacent surface of the tooth or tooth representation. The shading
may provide for maximizing the precision and or reliability of a
subsequent automatic recognition of a flat. This is because the shading
may provide a clear signal to an optical capturing device, like a camera
for example, and thus may be recognized in detail at a minimized error
level.

[0025] In a further embodiment the step of evaluating the first tooth flat
comprises automatic recognition of the first tooth flat by use of a
computer. For example the representation of the patient's first tooth may
be explored for a surface area which has a certain curvature within a
predetermined range, and a surface area having such a curvature may be
identified as flat. Such exploration may be performed manually, for
example at a physical model by a dental technician. Further the
exploration may be performed automatically for example by a computer
using a computer model obtained from previously scanning all or portions
of the patient's first tooth (with the patient's first tooth for example
provided in the form of a representation of the patient's tooth). However
the computer may also use a computer model obtained from real-time
scanning smaller portions of the patient's first tooth (with the
patient's first tooth for example provided in the form of a
representation of the patient's tooth).

[0026] In one embodiment the method comprises the step of determining at
least one positional relationship between the upper and lower jaws in
which the upper and lower jaws are under occlusal contact. The positional
relationship between the upper and lower jaws may be provided manually,
for example by a bite registration or by models of each the upper and
lower jaw joined in a certain position. This may facilitate calculating
the articulation, and thus may minimize computer processing time. The
step of determining a positional relationship may further comprise
detecting (for example automatically detecting) a second tooth flat at an
opposite second tooth on the basis of similar characteristic data between
the first and second teeth. The second tooth may be represented in a
computer model. Again such a computer model may represent one or more
further teeth, for example all teeth of one or both jaws, and part of the
gums.

[0027] In one embodiment the characteristic data comprise at least one of:

[0028] an inclination angle of the flat in a reference coordinate system;

[0029] a position of the flat in the reference coordinate system;

[0030] a curvature of the flat;

[0031] a surface roughness of the flat;

[0032] a size of the flat;

[0033] a shape of the flat; and

[0034] a normal on the flat.

[0035] The method may comprise the step of determining a motion path
representing a model of a possible movement of the jaws relative to one
another under occlusal contact. Thereby the motion path preferably
extends along a line between a first and a different second positional
relationship of the jaws. The occlusal contact may be provided between a
first set of teeth in a first positional relationship, and between a
different second set of teeth in a second positional relationship. The
occlusal contact may for example change along the motion path from the
first set of teeth to the second set of teeth, and eventually may be
provided at further different sets of teeth in between. The motion path
may be represented by a line or by multiple lines (for example lines
which together form a polygon). A line may be defined by any suitable
parameters, for example by the positions of two points on the line, or by
the position of one point on the line and a slope or direction vector.
Such a line may thus be a virtual line represented by parameters defining
the line.

[0036] In another embodiment the method may comprise the step of
determining a motion surface representing a model of a possible movement
of the jaws relative to one another under occlusal contact. The motion
surface may extend between at least three different positional
relationships between the jaws. A surface may also be defined by any
suitable parameters, for example by the positions of three points on the
surface, or by the position of one point on the surface and two slopes or
direction vectors. Such a surface may thus be a virtual surface
represented by parameters defining the surface.

[0037] In one embodiment the motion path or motion surface is used for
determining a shape of at least part of a dental restoration. For example
a jaw motion may be simulated virtually and the motion of points on one
or more teeth opposite the tooth to be restored may be used to define at
least part of an occlusal surface of the dental restoration. For example
at least a partial representation of a tooth opposite of the dental
restoration may be virtually moved on the motion path or on the motion
surface to virtually carve away a volume of a preliminary representation
of the dental restoration.

[0038] In a further embodiment the method comprises the step of providing
a representation of a preliminary representation of a dental restoration.
The representation of a preliminary representation may be selected from a
database holding a plurality of standard tooth shapes, for example.

[0039] In another embodiment the method comprises the steps of determining
a plurality of tooth flats at a patient's teeth or representations
thereof, and evaluating the plurality of tooth flats to provide
characteristic data representing a multiplicity of geometric
characteristics related to the individual tooth flats. Thereby the
accuracy of the determination of the articulation maximized. This may
further help minimizing computer processing time required for such
determination. In a further aspect the invention relates to a system for
preparing a dental restoration. The system comprises software adapted for
performing the method of the invention. The system may further comprise
at least one of a scanner, a CAD computer and a manufacturing machine for
a dental restoration.

[0040] In still a further aspect the invention relates to a use of one or
more tooth flats for providing a computer model of a patient's possible
jaw motion under occlusal contact between teeth in the patient's upper
and lower jaws. In this use a first tooth flat at a representation of the
first patient's tooth is determined and evaluated to provide
characteristic data representing at least one geometric characteristic of
the first tooth flat, and wherein the characteristic data is used to
calculate the possible jaw motion. This preferably makes the use of a
mechanical or virtual articulator unnecessary.

BRIEF DESCRIPTION OF THE FIGURES

[0041] FIG. 1 is a perspective top view of a plaster model of a patient's
teeth indicating tooth flats according to an embodiment of the invention;

[0042] FIG. 2 is a perspective view of a computer representation of a
patient's teeth indicating tooth flats according to an embodiment of the
invention;

[0043] FIG. 3 is a schematic view illustrating two teeth in occlusal
contact at tooth flats; and

[0044] FIG. 4 is a perspective view of a computer representation of a
portion of the upper and lower jaws of a patient used for preparation a
dental restoration according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The Figures describe an exemplary workflow of the method according
to the invention.

[0046] FIG. 1 shows a plaster model 10 representing a patient's teeth.
Such a plaster model can be typically obtained by taking a dental
impression from the patient's teeth, and using the impression to form the
plaster model. The dental impression is typically formed by placing a
hardenable, initially liquid or pasty, impression material in a patient's
mouth, allowing the material to harden in place, and finally removing the
hardened, preferably elastic, material from the patient's mouth. Thus a
negative impression of the patient's teeth may be formed that may then be
used as a mold for the plaster. A plaster preparation may for example be
filled in the negative impression and allowed to harden therein so that
finally a plaster model may be obtained like the one shown in the Figure.
The person skilled in the art will recognize that instead of or in
addition to the plaster model the negative impression may be directly
used in the method of the invention, although the use of a positive model
may have certain advantages.

[0047] The teeth in the plaster model 10 have tooth flats 11 which in the
example are indicated as patterned area. The person skilled in the art
will recognize that more flats may be present at one or more of the
patient's teeth, and that only some may be highlighted and illustrated in
this example.

[0048] The plaster model may be placed in a scanner, for example a dental
scanning device, which may capture the shape of at least a portion of the
plaster model (or the negative impression). Such a scanner is for example
available under the designation Lava® Scan ST from 3M ESPE AG,
Germany, or under the designation D700 from 3Shape A/S, Denmark, or under
the designation 5Series from Dental Wings, Canada. Thus the scanner may
indirectly capture at least a portion of the patient's teeth. The person
skilled in the art will further recognize that the shape of the patient's
teeth may be scanned directly in a patient's mouth, for example by use of
an intra oral scanner. Such an intra-oral scanner is for example
available under the designation Lava® COS from 3M, USA, or under the
designation E4D from D4D Technologies, USA, or under the designation
CEREC Bluecam from Sirona Dental Systems GmbH, Germany. The scanner
preferably uses the captured shape to provide scan data which represent
the outer surface of at least a portion of the patient's teeth.

[0049] The scan data may be processed in a computer which is adapted to
recognize the flats, for example to automatically recognize the flats.
For example the software may recognize contiguous surface areas having a
certain minimum size and a certain maximum curvature as flats.

[0050] Further the flats may be manually recognized and physically
highlighted before scanning, for example during an inspection of the
plaster model by a person. Such a highlighting may for example be made by
marking with a color which differs from the color of the plaster model.
The so prepared plaster model may be scanned with the scanner not only
capturing the shape of the model, but further capturing the shading or
color of the model surface. A direct highlighting of the natural teeth in
a patient's mouth as well as the highlighting of the impression is
possible. For highlighting natural teeth a substance may be used that is
transparent under normal light conditions, but optically detectable under
special light conditions. Such a substance may for example comprise
fluorescent particles that are substantially not visible under visible
light of a wavelength between 400 nm to 700 nm, but can be made visible
for the scanner under light of a shorter wavelength (for example under
infrared light). The substance may further be generally harmless and
water soluble so that it can be rinsed away easily when desired. Such a
substance may further be used for highlighting flats at the plaster model
or the negative impression. Further the computer aided and manual
recognition of the flats may be combined. This may help maximizing the
reliability of recognizing the flats.

[0051] FIG. 2 shows a surface representation 10' of the patient's teeth as
it may be generated by the computer based on the scan data. The surface
representation 10' comprises flats 11' recognized by the computer which
in the Figure are highlighted for better illustration. The computer may
be adapted to display the surface representation 10' on a computer
screen, and further to display the flats as highlighted areas to make the
flats clearly visible to a user. However the flats may be also be
recognized within the computer without visualizing them. The computer may
further allow a user to select or deselect individual flats from the
flats displayed. For example the computer may allow the user to select a
flat or multiple flats that should be used in a subsequent step of the
method of the invention, or to deselect a flat for excluding it from use
in a subsequent method step. A certain flat may for example further be
deselected if it was erroneously recognized as a flat. Such a function
may for example be implemented such that a user can position a mouse
cursor on the flat and clicking it for selection or deselection. Selected
and deselected flats may be indicated to the user by different colors
and/or patterns, for example.

[0052] A recognized or selected flat may further be evaluated to provide
corresponding characteristic data about the flat. Such characteristic
data may for example comprise at least one of the following data:

[0053] shape of the flat;

[0054] size (for example area) of the flat;

[0055] position of the flat relative to a reference coordinate system;

[0056] an inclination angle of the flat in one or more dimensions of a
reference coordinate system; and

[0057] a normal on the flat.

[0058] The characteristic data may be used to determine one or more
constraints in a possible movement of a patient's upper and lower jaw
relative to each other. Further the characteristic data may be used to
define one or more positional relationships between the upper and lower
jaw, for example a position in which the jaws may be in occlusal contact,
meaning a position in which at least one tooth of the upper jaw and at
least one tooth of the lower jaw can be in contact in the patient's
mouth.

[0059] FIG. 3 shows an upper tooth 12 of an upper jaw and a lower tooth 13
of a lower jaw. The upper tooth 12 has a first flat 14 and a second flat
15. The positions of the first and second flats 14, 15 also define
positions in which the upper and lower jaws can be in occlusal contact
(as illustrated) because the flats 14, 15 may result from abrasion
between teeth of the upper and lower jaw which requires such contact.

[0060] Further the shape and size of a flat may be used to detect a flat
of a similar shape and size at an opposite tooth which may provide a
positional relationship between the upper and lower jaws. In the example
the lower tooth 13 has first and second flats 16, 17 which approximately
correspond in size and shape to the first and second flats 14, 15 of the
upper tooth 12. Thus the first and second flats 14, 15 and the flats 16,
17 may be assigned or matched to one another. Such an assignment or
matching may be performed virtually, for example by computer processing.
In this way one possible positional relationship between the upper and
lower jaws may be determined.

[0061] In another example an occlusal position may be provided by a bite
registration. Typically a bite registration comprises at least a partial
impression of the patient's teeth in at least one occlusal position. Such
a bite registration may be provided by a dentist, for example. The bite
registration may be scanned directly, or indirectly from a plaster model
molded by use of the bite registration. A surface representation of the
bite registration may be electronically matched with surface
representations of teeth of the upper and lower jaw. Thus the positional
relationship between the upper and lower jaw in at least one occlusal
position may be determined.

[0062] The inclination angle of a flat may define a direction in which the
upper and lower jaws are movable relative to one another when the jaws
are in a certain positional relationship. This is indicated by the arrow
18 in the Figure. The flats 14, 15, 16, 17 are all inclined at a similar
angle from which a certain direction of movement between the jaws under
occlusal contact may be assumed.

[0063] The computer may perform an iterative process in which possible
positional relationships and possible movements of the upper and lower
jaw relative to each other are determined by use of the characteristic
data. Preferably a plurality of flats may be used to determine a
multiplicity of characteristic data. Thus a multiplicity of occlusal
positions and directions of movement may be obtained to form articulation
data.

[0064] Such articulation data may be used to create an articulation
profile defining a motion path on which the jaws may move, while in
occlusal contact, relative to one another. For defining the motion path
at least two occlusal positions may be used with the motion path being
defined by a straight line between the positions. Further such motion
path may correspond to a spline defined by several positions in which the
upper and lower jaws may be in occlusal contact. The occlusal positions
used to define the articulation profile may be determined by help of the
directions of movement, for example by detecting a second occlusal
position in the proximity of a certain direction of a first occlusal
position. A plurality of articulation profiles may be used to provide an
articulation surface. The articulation surface may be defined by a
surface between at least two articulation profiles. Such a surface may be
approximated by a set of straight lines (or curved lines, for example
obtained from a spline) extending between the profiles. Thus the
articulation surface may be approximated by a set of lines forming a
virtual three-dimensional wireframe. In this way an approximate
representation of the articulation of a patient's jaws may be determined
in at least a certain range without the use of an articulator.

[0065] Further a generic model of a temporomandibular joint may be defined
by use of the articulation data. For example from the shape of one or
more articulation profiles or the articulation surface approximate joint
positions of the temporal bone and the mandible of the upper and lower
jaws respectively may be determined.

[0066] In a further example plaster models of upper and lower jaws of a
patient may be brought in occlusal contact with one another. An occlusal
contact as it can occur in a patient's mouth may be determined by
positioning the models such that a flat of one tooth contacts an opposing
tooth or a corresponding flat of that opposing tooth. This may for
example be done manually by an operator. The plaster models of the
patient's jaw may further be brought in occlusal contact with one another
in a plurality of different positional relationships of the models
relative to one another. Each positional relationship of the plaster
models may be captured, for example by scanning the plaster models while
in occlusal contact. Thus a plurality of positional relationships of the
jaws relative to one another may be determined and used to calculate a
possible jaw motion or articulation.

[0067] FIG. 4 illustrates a computer representation of an upper jaw 20 and
a lower jaw 30. The lower jaw 30 comprises a computer representation of a
dental restoration 31. A preliminary representation of the dental
restoration may be obtained from a database holding a plurality different
standardized tooth shapes. The preliminary representation of the dental
restoration may for example be selected from the database on the basis of
the location of the tooth to be restored, for example dependent on
whether the tooth is located in the upper or lower jaw and dependent on
the position (front, left or right side) in the jaw. The preliminary
representation of the dental restoration may be changed at the lateral
sides by computer aid, for example by use of a dental CAD system, so that
it pleasantly fits inline with adjacent teeth. The occlusal side of the
preliminary representation of the dental restoration may be initially
oversized such that it overlaps with one or more opposing teeth in at
least one positional relationship of the jaws under virtual occlusal
contact (indicated by numeral 32). The overlap may be automatically
removed by computer aid such that the preliminary representation of the
dental restoration is trimmed. Thereby the preliminary representation may
obtain the negative shape of the opposing tooth or teeth or a proximate
of it. The removal of overlap may be repeated at different positional
relationships of the upper and lower jaws relative to one another. For
example the different positional relationships of the jaws may be
selected according to one or more motion paths and/or to one or more
motion surfaces (as indicated by the array of arrows 33). Thus the
preliminary representation of the dental restoration may be virtually cut
due to a relative movement between the preliminary representation and the
opposing teeth. Therefore the trimmed preliminary representation may not
collide with opposing teeth in a variety of positional relationships of
the jaw. The skilled person will recognize that the removal of the
overlap may comprise providing a small space between the trimmed dental
restoration representation and the opposing tooth or teeth. This may
avoid for interferences between the final dental restoration and opposing
teeth, for example which may arise due to tolerances during manufacturing
of the dental restoration or during placement of the dental restoration
in a patent's mouth.

[0068] The skilled person will be able to provide further methods of
shaping a representation of a dental restoration. For example the
preliminary representation of the dental restoration may be obtained by
automatic or manual design, by scanning at least a portion of the tooth
to be restored, or a combination thereof. Further instead of trimming an
oversized representation an undersized preliminary representation may be
virtually grown until it virtually abuts the surface of one or more of
the opposing teeth. It may also be possible to provide a final
representation of a dental restoration without starting at a preliminary
representation. For example the constraints provided by the teeth
opposing the tooth to be restored may be used to automatically create a
representation of the occlusal face of the dental restoration. This
representation of the occlusal face may then be automatically completed
by lateral faces, for example shaped according to constraints provided by
a tooth or teeth adjacent the tooth to be restored.

[0069] The trimmed, grown, automatically created, or preliminary
representation of the dental restoration may further be provided with
fissure structures, for example manually by using a CAD System, to make
the final dental restoration resemble a natural tooth.

[0070] After shaping the representation of the dental restoration a final
representation of the dental restoration may be obtained in the form of
computer data. Such computer data may be used to provide machine
instructions for controlling a machine, for example a milling, grinding
or rapid prototyping machine, to manufacture a physical dental
restoration.

[0071] The physical dental restoration may be a precursor of a
pre-sintered ceramic material which may be sintered and optionally
veneered or provided with a glaze to obtain the final dental restoration,
for example. However the physical dental restoration may already
correspond to the final dental restoration for example milled or ground
from a finally sintered ceramic block.